add clide ui open to drive GUI readers from the CLI (T-231)

The drive-half complement to clide status (observe): an agent can now
open a doc in a GUI reader from the CLI so it can show the user what
it's looking at. 'clide ui open tickets T-48' (decisions by id,
markdown by path) publishes a 'selection' to the kernel MessageBus that
the reader's ReaderNav picks up.

The verb (ui_command.dart) is decoupled from the kernel via a publish
callback, wired in main.dart to the post-boot-captured MessageBus, so it
stays Flutter-free under dart test. Reads CLI positionals or named args.

Also files T-232 (CLI argv args don't reach typed handlers -- the gating
drive-the-IDE bug) and T-233 (diff-panel ui.open follow-up).

Closes T-231 (under T-208).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/src/daemon/ui_command.dart

@@ -0,0 +1,72 @@
+/// Registers `ui.open` — the drive-half of D-6 parity (T-231).
+///
+/// Epic C (T-218) gave the CLI the *observe* half: `clide status` / `pane
+/// list` read live UI state. This is the complement — the agent asks the
+/// GUI to open a doc in one of its readers, so it can say "look at this
+/// with me." Opening a reader doc is otherwise a UI-only action (a click
+/// publishes a `selection` to the kernel MessageBus); this verb publishes
+/// the same message from the CLI.
+///
+///   clide ui open tickets   T-48
+///   clide ui open decisions D-17
+///   clide ui open markdown  docs/initial-plan.md
+///
+/// The handler is decoupled from the kernel: it takes a [MessagePublisher]
+/// callback (wired to the MessageBus in main.dart), so this file stays
+/// Flutter-free and runs under `dart test`.
+library;
+
+import '../ipc/envelope.dart';
+import '../ipc/schema_v1.dart';
+import 'dispatcher.dart';
+
+/// Publishes a message to the kernel MessageBus. `void Function(publisher,
+/// channel, data)` — the tear-off of `MessageBus.publish`.
+typedef MessagePublisher = void Function(String publisher, String channel, Map<String, Object?> data);
+
+/// The readers `ui.open` can target → (bus publisher id, payload key the
+/// reader reads its entry from). Matches each reader's `ReaderNav` dataKey
+/// (tickets/decisions key on `id`; markdown on `path`).
+const Map<String, ({String publisher, String dataKey})> _readers = {
+  'tickets': (publisher: 'builtin.tickets', dataKey: 'id'),
+  'decisions': (publisher: 'builtin.decisions', dataKey: 'id'),
+  'markdown': (publisher: 'builtin.markdown', dataKey: 'path'),
+};
+
+void registerUiCommands(DaemonDispatcher d, MessagePublisher? Function() publisher) {
+  d.register('ui.open', (req) async => _open(req, publisher));
+}
+
+IpcResponse _userErr(String id, String message, {String? hint}) => IpcResponse.err(
+      id: id,
+      error: IpcError(code: IpcExitCode.userError, kind: IpcErrorKind.userError, message: message, hint: hint),
+    );
+
+Future<IpcResponse> _open(IpcRequest req, MessagePublisher? Function() publisherSource) async {
+  // Accept CLI positionals (`ui open <reader> <ref>`) or named args.
+  final positional = (req.args['positional'] as List?)?.whereType<String>().toList() ?? const <String>[];
+  final reader = (req.args['reader'] as String?) ?? (positional.isNotEmpty ? positional[0] : null);
+  final ref = (req.args['ref'] as String?) ?? (positional.length > 1 ? positional[1] : null);
+
+  if (reader == null) {
+    return _userErr(req.id, 'reader is required', hint: 'one of: ${_readers.keys.join(', ')}');
+  }
+  final target = _readers[reader];
+  if (target == null) {
+    return _userErr(req.id, 'unknown reader: $reader', hint: 'one of: ${_readers.keys.join(', ')}');
+  }
+  if (ref == null || ref.isEmpty) {
+    return _userErr(req.id, 'a doc id/path is required (e.g. `ui open $reader <ref>`)');
+  }
+
+  final publish = publisherSource();
+  if (publish == null) {
+    // No live UI bus — headless / CLI-only context. Honest failure, not a hang.
+    return IpcResponse.err(
+      id: req.id,
+      error: IpcError(code: IpcExitCode.toolError, kind: IpcErrorKind.toolError, message: 'no live UI to drive (clide is not running a GUI)'),
+    );
+  }
+  publish(target.publisher, 'selection', {target.dataKey: ref});
+  return IpcResponse.ok(id: req.id, data: {'reader': reader, 'ref': ref, 'opened': true});
+}